class Solution
{
public:
    int maxProfit(vector<int> &prices)
    {
        int n = prices.size();
        vector<vector<int>> dp(n, vector<int>(2));
        dp[0][0] = -prices[0];
        for (int i = 1; i < n; ++i)
        {
            dp[i][0] = max(dp[i - 1][0], 0 - prices[i]);
            dp[i][1] = max(dp[i - 1][1], dp[i - 1][0] + prices[i]);
        }
        return max(dp[n - 1][0], dp[n - 1][1]);
    }
};
class Solution
{
public:
    int maxProfit(vector<int> &prices)
    {
        int n = prices.size();
        vector<vector<int>> dp(n, vector<int>(2));
        dp[0][0] = -prices[0];
        for (int i = 1; i < n; ++i)
        {
            dp[i][0] = max(dp[i - 1][0], dp[i - 1][1] - prices[i]);
            dp[i][1] = max(dp[i - 1][1], dp[i - 1][0] + prices[i]);
        }
        return max(dp[n - 1][0], dp[n - 1][1]);
    }
};
class Solution
{
public:
    int maxProfit(vector<int> &prices, int fee)
    {
        int n = prices.size();
        vector<vector<int>> dp(n, vector<int>(3));
        dp[0][0] = -prices[0] - fee;
        for (int i = 1; i < n; ++i)
        {
            dp[i][0] = max(dp[i - 1][0], dp[i - 1][1] - prices[i] - fee);
            dp[i][1] = max(dp[i - 1][1], dp[i - 1][0] + prices[i]);
        }
        return max(dp[n - 1][0], dp[n - 1][1]);
    }
};
class Solution
{
public:
    int maxProfit(vector<int> &prices)
    {
        int n = prices.size();
        vector<vector<int>> dp(n + 1, vector<int>(3));
        dp[0][0] = -prices[0];
        for (int i = 1; i <= n; ++i)
        {
            dp[i][0] = max(dp[i - 1][0], dp[i - 1][1] - prices[i - 1]);
            dp[i][1] = max(dp[i - 1][1], dp[i - 1][2]);
            dp[i][2] = dp[i - 1][0] + prices[i - 1];
        }
        return max(dp[n][0], max(dp[n][1], dp[n][2]));
    }
};
class Solution
{
public:
    TreeNode *pruneTree(TreeNode *root)
    {
        if (root == nullptr)
            return nullptr;
        root->left = pruneTree(root->left);
        root->right = pruneTree(root->right);
        if (root->left == nullptr && root->right == nullptr && root->val == 0)
            return nullptr;
        else
            return root;
    }
};
class Solution
{
public:
    long long int prev = LONG_MIN;
    bool isValidBST(TreeNode *root)
    {
        if (root == nullptr)
            return true;
        int left = isValidBST(root->left);
        if (left == false)
            return false;
        int cur = false;
        if (root->val > prev)
        {
            cur = true;
            prev = root->val;
        }
        if (cur == false)
            return false;
        int right = isValidBST(root->right);
        return left && right && cur;
    }
};